1. Field of the Invention
The present invention relates to semiconductor switch devices, and more particularly to improvements in power semiconductor devices, e.g., power transistor switch devices, comprising a current transformer for supplying the control electrode current, e.g., the base current.
2. Description of the Prior Art
Power semiconductor switch elements, such as power transistors, must maintain the control electrode current in order to maintain the conductivity of the main current. Large power semiconductor switch elements require intricate means for supplying the control electrode current. Such control electrode current must be large enough to cope with the heaviest possible operating load. To supply a large control electrode current with high efficiency, prior art techniques have proposed the use of a current transformer to thereby self-supply (or replenish) the control electrode current in response to the main current such as the load current and the power switch current. The conventional method for self-supplying the control electrode current by the use of a current transformer depends on an inverter system because the current transformer is only capable of handling AC and not DC components of current.
Prior art techniques have failed to provide systems for supplying the control electrode current through a current transformer in combination with a DC power control chopper, a variable frequency converter or the like, for operation over a wide range of turn-on time ratio.